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Magnetic detecting device and material identifying device

a magnetic detection and material technology, applied in the direction of magnetic property measurement, material magnetic variables, instruments, etc., can solve the problems of inability to apply methods, objects that are not being conveyed, and inability to obtain measurements instantaneously, so as to prevent a magnetic field induced, reduce the effect of noise components, and improve repeatability

Inactive Publication Date: 2009-04-28
UNIV OKAYAMA
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

Enables accurate and instantaneous detection of both ferromagnetic and non-ferromagnetic materials without magnetizing unintended items, while minimizing the effects of high-frequency fields, allowing for real-time identification of complex objects and reducing noise interference.

Problems solved by technology

With a method of measuring a phase change as a means for analyzing a complex test object such as meat containing a misplaced metal piece, results of measurement cannot be obtained instantaneously because there is a need for measuring the complex test object flowing on a belt conveyor for a certain length of time to obtain a time change.
As a result, this method cannot be applied, for example, to objects that are not being conveyed.
Further, there is a problem in the method for detecting a dangerous article by magnetizing ferromagnetic material such as iron that materials which are not supposed to be detected are also magnetized.
However, leaving out of consideration response characteristics for frequency changes in the applied magnetic field, an analysis cannot be made, for example, of a complex object containing magnetic and nonmagnetic materials.
However, there is a problem at issue of effects of high frequency magnetic fields being applied to a human body.
Although the effects of high frequency magnetic fields have not yet been quantified, there has been found a negative impact, for example, of heat generated with an eddy current in a human body induced by a high frequency magnetic field.

Method used

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  • Magnetic detecting device and material identifying device
  • Magnetic detecting device and material identifying device
  • Magnetic detecting device and material identifying device

Examples

Experimental program
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Effect test

embodiment 1

[0084]FIG. 1 is a schematic diagram showing a basic configuration of a magnetic detecting device according to the present invention. A magnetic field is applied by an apply coil 1 in order to measure a magnetic response of a test object 9. The frequency of the applied magnetic field can be changed by a power source 2 for the apply coil with the use of a signal sender 4. The generated signal drives a current source 3 to apply an alternate current to the apply coil 1. A change in the magnetic field induced by the test object 9 is detected by means of a magnetic sensor 5 comprising a magnetoresistance element. As a matter of course, any one of a magnetic impedance effect sensor, a flux gate, a superconducting quantum interference device can also be used instead. Environmental magnetic noises including the terrestrial magnetism is also input to the magnetic sensor 5, as well as the magnetic field from the test object 9. Not only that, the applied magnetic field is also applied to the ma...

embodiment 2

[0087]FIG. 3 is a schematic diagram showing a configuration of a coil of a magnetic detecting device according to a second embodiment of the present invention. The second embodiment relates to the magnetic detecting device according to the first embodiment, wherein the cancel coil 6 is separated into an apply coil magnetic field cancel coil 20 and a direct magnetic field cancel coil 21, and the apply coil magnetic field cancel coil 20 is connected to the power source 2 for the apply coil with the serially connected apply coil 1. Because the apply coil magnetic field cancel coil 20 and the apply coil 1 are connected in series, magnetic fields generated by the two coils have the same frequency. Consequently, adjustment is not required for the purpose of cancellation.

embodiment 3

[0088]FIG. 4 is a schematic diagram showing a basic configuration of a magnetic detecting device according to a third embodiment of the present invention. In the third embodiment there is provided a distance measurement means 22 for determining positions of the test object 9 and the apply coil 1. The distance measurement means 22 may be placed anywhere, either near the apply coil 1 or the magnetic sensor 5, provided that relative distances between the distance measurement means 22 and both the apply coil 1 and the magnetic sensor 5 are known. A magnetic response from the test object 9 for the applied magnetic field varies according to the distance from the apply coil 1, and the intensity of the signal differs greatly according to the distance from the magnetic sensor 5 for detecting the magnetic response. Thus, measurement can be carried out with higher repeatability by providing the distance measurement means 22.

[0089]FIG. 5 is a diagram showing a correspondence between the applied...

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Abstract

The present invention discloses a magnetic detecting device comprising an apply coil 1 for generating an alternate magnetic field of variable frequency and a power source 2 for the apply coil; a magnetic sensor 5 for detecting a change in the magnetic field induced by a test object 9 placed at a distance from a surface of said apply coil and toward said test object, said magnetic sensor being provided with a cancel coil 6 for canceling a magnetic field generated at the position of the magnetic sensor by a direct magnetic field and / or said apply coil; a measurement circuit 7 for the magnetic sensor for measuring a detection signal of said magnetic sensor; a lock-in amplifier circuit 8 for detecting an output of said measurement circuit for the magnetic sensor into two signals having the same frequency as that of said apply coil and phases different from each other by 90 degrees; and an analysis means 10 for analyzing a phase change of the output of said magnetic sensor 5 using an output signal from said lock-in amplifier circuit 8.

Description

TECHNICAL FIELD[0001]The present invention relates to a device for applying an alternate magnetic field to a test object and detecting response characteristics thereof using a magnetic sensor.RELATED ART[0002]A metal detector is known as a device for applying an alternate magnetic field to examine the response characteristics. The metal detector comprises a search coil that generates an alternate magnetic field to generate an eddy current on a metal surface of the test object, which in turn generates a magnetic field repulsive to the applied magnetic field. Since this magnetic field changes an electromotive force in response to changes in the magnetic flux penetrating through the search coil, as may be represented using Faraday's law of electromagnetic induction, existence of metal can be detected by measuring the changes in a signal. Also known are methods of nondestrucive inspection such as a method for inspecting a defect in a steel pipe or a wire rope by generating an eddy curre...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): G01R33/12
CPCG01N27/72G01V3/104
Inventor TSUKADA, KEIJIKIWA, TOSHIHIKO
Owner UNIV OKAYAMA
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